Apparatus for evacuating and sealing



Oct. 30, 1956 J. w. DAWSON ET AL 2,768,490

' APPARATUS FOR EVACUATING AND SEALING Filed Dec. 29, 1953 PULSERESISTANCE 52- WELDER I INVENTORS JOHN w. DAWSON geBERT C. INGRAHAMATTORNEY United States Patent "ice 2,768,490 APPARATUS FOR EVACUATINGAND SEALING John W. Dawson, Winchester, and Robert C. Ingraham,

Danvers, Mass, assignors to Sylvania Electric Products Inc., acorporation of Massachusetts Application December 29, 1953, Serial400,997

2 Claims. (Cl. 553-101) The present invention is drawn to methods andapparatus for sealing electrical devices in hermetically sealed andevacuated envelopes and more particularly for evacuating and sealing theenvelopes ofv semiconduotor devices such as diodes for rectification andtransistors for amplification and the like. Such devices usually includeone or more rectifying contacts on a body of semiconductor whichordinarily h a-s connection.

It has for some time been apparent that even amount of ordinaryatmosphere enclosed in the sealed envelopes of such devices might intime have deleterious possible the thorough evacuation of such envelopesfor sealing and, if desirable, the filling of such devices with a rareor other inert gas. V I

Diodes and transistors employing germanium and like semiconductivematerials are inherently susceptible to fiabrication as very 'tinyunits. The space that might be occupied and the complexity that might beintroduced by an exhaust tubul-ation is objectionable from the point ofview of compactness and simplicity of manufiacture; and accordingly itis a further object of the invention to avoid the need for suchexhausttubulation in fabricating evacuated (and optionally refilled) sealedunits. The envelope 'of an inherently tiny device could have no morethan a small exhaust tubulation. A protracted time is required forexhausting an envelope to any specified highorder vacuum through a verysmall-diameter tube; or, viewed otherwise, the degree of vacuumresulting when a small-bore exhaust tubulation is used isrelativelypoor. By virtue of the present invention which avoids the exhausttubulation entirely, a high-grade vacuum may be effected quickly.

As will be seen, the illustrative embodiment of the apparatus aspect ofthe invention includes a two-element chamber wherein locating andholding portions are pro vided for respective parts of a two-partenvelope; and the part-holding portion of one element of the chamber ismovable relative to the chamber in the way to appreach the envelope partheld by the other element of the chamber. The chamber incorporatessealing means effective to unite and hermetically seal the envelopeparts together, optionally by induction-heating to melt solder or thelike on the opposed envelope parts (as in copending application SerialNo. 390,068, filed November 3, 1953, by Frederic Koury); or the envelopeparts, evacuated while separated, are brought into assembled contact andresistance-welded, as detailed below or they may be united by acold-flow process now well known.

The nature of the invention and its further features of novelty will bebetter appreciated from the following detailed disclosure of anillustrative embodiment. In the drawings,

Fig. 1 is a fragmentary view, greatly reduced in scale,

2,768,490 Patented Oct. 30, 1956 of novel apparatus embodying featuresof the invention;

Fig. .2 is a longitudinal cross-sectional view, somewhat reduced, of apart of the apparatus of Fig. 1, cmbodying features of the invention;

Fig. 3 is a view similar to Fig. 2 of the same device at another phaseof its operation;

Fig. 4 is an enlarged detail of the apparatus in Fig. 3; and

Fig. 5 is an enlarged cross sectional view of a typical devicefabricated by means of the present invention.

Referring now to Figs. 2-4 inclusive it is seen that a two-elementchamber 10A and 10B is shown in which the lower element 10B has anexhaust line 12 which branches int-o passages 14 and 16 communicatingwith the hollow18 in chamber element 10A. A rubber ring 20 which issuitable for forming a seal between elements 10A and 10B of the chamberalso introduces electrical insulation between those chamber elements. Arigid ring 22 of suitable insulation is carried by chamber element 103for guiding element 10A along the vertical axis of chamber element 10B.Ring 22 is received in relief 24 of chamber element 10A. A key 26, alsoof insulation, is secured to chamber element 10B, and is slidablyreceived in groove 28in the upper chamber element 10A.

At the top of element 10A is a metal sylphon bellows 30 having aninternal stiff helical compression spring 32 and a vertically slidableshaft 34 therein, this shaft being held against rotation in its supportby-a pin and slot connection 36.

As seen in Fig. 4, chamber element 10 B includes an insert 38 of anysuitable electrically conducting material which is formed with a seatshaped to receive lower part 40 of a typical device to be evacuated andsealed. The upper part 42 of the device is received in a recess 44within slide member 34; and member 42 is held frictionally in place by aspring-ball detent 46. Member 34 is also electrically conductive. I

In Fig. 5 the illustrative device being fabricated in the apparatus ofFigs. 2-4 is seen to be a point contact transistor including a flangedmetal ring 40a, three leads 40b extending through a glass seal 40c; andsharp rectifying contacts 40d are carried by two of the leads 40b,bearing against a semiconductor body 40:: which is carried by andohmically united to the third lead 401;. Glass seal 40c and flangedmetal ring 40a constitute the lower envelope part, received in element10A of the chamber.

The upper envelope part 42 of the device has a flange 42a which is to beunited and hermetically sealed to the flanged ring 40a of the lower part40. The completed unit as shown in Fig. 5 has a continuous weld, as willbe described, and the space occupied by the contacts 40b and body 40c isevacuated or filled with an inert gas to any desired degree pressure andof any desired composition. A very high vacuum -or a very pure rare gasboth have features to recommend them.

In Fig. 1 there is shown part of a conveyor 50 on which is carried aseries of lower cavity members 10B spaced at regular intervals. Thisconveyor 50 is suitably provided with an intermittent mechanism (notshown) for "advancing it stepwise, involving details well known andforming no part of the present invention. The conveyor may take the formof an endless belt or it may simply be a stepwise indexed plate orturret. The exhaust line 12 is similarly shown broken away because themechanisms for connecting such lines to a suitable exhaust system afterleaving a first loading station, is Well known in machines that havelong been used in exhausting and sealing vacuum tubes. Such machinesalso connect rare gas supplies to the exhaust lines at suitable times,after evacuation but before sealing in the present instance.

At the third station of Fig. 1 there is shown a resistance welding powersupply 52 electrically connected to switch 54 between the conveyor 50(connected to all of the lower chamber elements 108) and additionallyconnected to :a ram 56 :slidable in bearing 58 and operated to compresssylphon bellows 30 at an appropriate time in the cycle. The actuatingmechanism for arm 60 may take the form of a cam or a solenoid or anair-operated piston or any suitable mechanism and is accordingly notshown in detail.

In operation the two-part chamber is manually separated as shown infirst station of Fig. 1, and the two portions of the device of Fig. areseparately inserted, manually, into the respective seats in parts 38 and44. At this first station, chamber element '10A'is physically assembledonto the lower chamber element B to occupy the position illustrated inFig. 2, with chamber element 10A resting on sealing ring and with theenvelope part 42 supported in proper opposed alignment with the lowerenvelope part 40 by virtue of ring 22 and key 26.

In the second station of Fig. 1 the chamber 10A, 10B isevacuated, to ahigh degree of vacuum as may be desired, with the interior of hollowmember 42 freely exposed to the vacuum system. Effective evacuation isassured and expedited by holding these two parts separated during theevacuating interval. During this time spring 32 maintains slide member34 in the upper position of Fig. 2.

There may be a sequence of stations represented by the single station atthe center of Fig. 1, as may be deemed expedient for progressivelyperfecting the evacuation of the'device; and an additional station maybe used if desired for introducing a rare gas by way of line 12 or byway of a separate tube not shown. Such details are well known in the artof vacuum tubes and are not illustrated.

When the degree of vacuum and optional filling has been completed, thetwo-part assembly 10A, 10B moves into the position shown at the right ofFig. 1. At this station actuator 60 forces slide 56 against slide 34 anddepresses that slide until flanged envelope part 42 bears firmly againstmetal ring 40a. Closure of switch 54, manually or by suitable automaticmeans, introduces a burst of welding current by way of rod 56, slide 34,members 42 and 42a, metal insert 38, and lower cavity member 10B. One ofthe metal parts may be formed with a rib, in order to facilitate forminga continuous projection weld as a hermetic seal. It is significant,perhaps, that the welding is effected in a chamber of minimal size andwithout manual access to the parts to be united; and it is furthersignificant that the welding heat is developed only in that limitedregion where it is desired, without unnecessarily exposing thesemiconductor to high temperatures. Such devices are susceptible todamage by excessive heat, so that the apparatus illustrated is es---pecially suitable for sealing such temperature-sensitive devices.

The illustrative embodiment of the invention, and the specificapplication shown, are naturally susceptible to a latitude ofmodification and to varied application. Acoordingly the appended claimsshould be broadly construed, as is consistent with the spirit and scopeof the invention.

What is claimed is:

1. Apparatus for evacuating and sealing semiconductor devices, includinga chamber having mutually separable elements, electrical insulationseparating one of said chamber elements from the other of said elements,retaining means in each chamber element for supporting respectiveenvelope parts of the device in spaced-apart positions, one of saidretaining means being movable relative to its chamber element to carryits retained envelope part against the other, means for evacuating thespace in and around the envelope parts, and means to impress a weldingcurrent on the assembled envelope parts.

2. Apparatus for evacuating and sealing together two parts 'of' ametallic envelope having registering weldable surfaces, including achamber defined by a pair of separable elements, electrical insulatingmeans separating one of said elements from the other, a vacuum outletfor said chamber in one of said elements, a first retaining means in oneof said elements for supporting one of said envelope parts in fixedposition with respect to said one element, a second retaining means inthe other of said elements for supporting the other of said envelopeparts spaced "from said one envelope part during evacuation of saidchamber, said second retaining means including a cylindrical slidemember movable in an opening in said other element and having a .recessin the end thereof within the chamber to receive at least a portion ofsaid other envelope part, means for moving said slide member toward saidfirst retaining means, thereby to force together'the registeringsurfaces of the envelope parts, and means for causing a Welding currentto flow through both of said retaining means and the envelope partssupported thereby.

References Cited in the file of this patent UNITED STATES PATENTS1,790,787 Badger Feb. 3, 1931 2,006,818 Zimber July 2, 1935 2,014,597Staley Sept. 17, 1935 2,223,031 Edwards Nov. 26, 1940 2,274,400 DeMargitta Feb. 24, 1942 2,435,747 Larson Feb. 10, 1948

